The proposed research is designed to describe in detail the relationships between different classes of axon terminals and specific neurons in the cat medial superior olivary nucleus and cochlear nuclei. A variety of light and electron microscopic methods including autoradiographic analysis of material from fresh brain slice preparations incubated with labeled amino acids will be used. The differential ability of cells and cellular elements to sequester labeled compounds derived from H3-amino acid putative neurotransmitter is being studied to identify and correlate chemical and ultrastructural characteristics of labeled elements and to illucidate the differential distribution of the various terminal classes on different neuronal types. Genetically caused alterations of the auditory system, including cochlear and brain stem neuronal groups, are being described in deaf white cats and C57BL/6 mice.